The present invention relates to a linear unit, especially an apparatus for the machining, transportation and manipulation of workpieces, with a housing and with a carriage which is movable out of the housing and to which a handling appliance or the like for the workpiece can be fixed.
Linear units of this type are known and are employed in commerce and industry when constantly recurring worksteps are to be performed. Such linear units can execute especially rectilinear movements. There are known units which have only two end positions and those which have one or more holding positions.
Such linear units are basically of approximately identical constitution and construction. Arranged in a housing is a carriage which possesses a carrier plate at one end, in particular where it comes out of the housing. To be mounted on such a carrier plate are appropriate tools, handling appliances, rotary units or the like which, for example, grasp a workpiece to be machined and bring it into the desired working position. The linear shift of the workpiece is preferably brought about by a pneumatic device which pushes the carriage out of the housing and moves it back again into the initial position.
In general terms, a carriage of this type consists of one, but preferably of two guide rods, to which the carrier plate is assigned on one side and which slide in corresponding bearings. The guide rods are often extended piston rods of pistons which set the carriage in motion.
However, a disadvantage often revealed in such units is that over relatively long strokes, especially during the machining of heavy workpieces, the carriage is no longer absolutely dimensionally stable. A corresponding distortion or bending of the guide rods makes it necessary to allow for undesirable inaccuracies which, though minimal, are nevertheless detectable.
A further disadvantage of such units is the arrangement of the limit stops. Since they are usually located outside the bearing plane of the carriage, high distortion forces likewise arise upon impact and can lead to dimensional inaccuracies or result in increased material wear.
A further serious disadvantage of the linear units of the type described above is that intermediate positions between the limit stops can be set only in specific regions and not over the entire stroke length. However, a simple continuous adjustment of intermediate stops over the entire stroke length is a requisite which repeatedly becomes necessary.
All these disadvantages show themselves during use to be either time-consuming, wearing on material or costly.